The level of radiation present at a location can change without warning. For example, a failure at a nuclear power plant or storage facility can result in a rapid increase in the level of radiation at the failure location.
While a large scale failure may be obvious to a person in the vicinity of the failure location, a small scale failure, such as a crack in a container filled with radioactive material, may be less apparent and may therefore go unnoticed for a period of time.
Likewise, there are situations in which the level of radiation at a location may increase gradually over time; for example, within pipes used for oil extraction. This is known as naturally occurring radiological material/matter (NORM).
Such formation of a radioactive location can be life threatening to a person in the vicinity of the radioactive location, especially if the person is unknowingly exposed to the radiation for a prolonged period of time.